4,4'-diaminodiphenyl methanes symmetrically substituted on the nucleus are known from a number of publications as chain-extending agents for use in the production of polyurethane urea elastomers. German Offenlegungsschrift No. 1,949,165 and U.S. Pat. No. 3,188,302 for example, describe chain-extending agents corresponding to the general formula: ##STR1## where R.dbd.H, --CH.sub.3, --OCH.sub.3, --COOCH.sub.3, --Cl. German Offenlegungsschrift No. 2,731,815 describes, for example, a chain-extending agent corresponding to the following formula: ##STR2## where R.dbd.CH.sub.3. These substituted aromatic diamines, however, are extremely difficult to process because of their high melting points.
The above-mentioned chain-extending agents may be divided into two groups in respect to their reactivity to isocyanates. The unsubstituted and alkyl-substituted diaminodiphenyl methanes react very quickly. Examples of these are 4,4'-diaminodiphenyl methane (melting point: 93.degree. C.), 3,3'-dimethyl-4,4'-diaminodiphenyl methane (melting point 156.degree. C.) and 3,3', 5,5'-tetramethyl-4,4'-diaminodiphenyl methane (melting point: 124.degree. C.). These high-melting chain-extending agents can only be processed in highly heated processing machines. These processes affect the operating personnel because of the heat given off and the vapors emanating from the amines (which are unavoidable even under clean working conditions). Because of their high reactivity, the above-mentioned diamines can only be machine-processed which, owing to the high melting point, also gives rise to machinery problems (for example crystallization of the diamines in pipes).
The relatively slow-reacting diamines are the second group of chain-extending agents. 3,3'-dichloro-4,4'-diaminodiphenyl methane (MOCA), which has a melting point of from 99.degree. to 107.degree. C., and 3,3'-dicarbomethoxy-4,4'-diaminodiphenyl methane which has a melting point of 146.degree. C. are examples of these. Although these products show such low reactivity as chain-extenders that they can be processed without using machines, their high melting points again cause problems. Because of their low reactivity, the cycle times in the production of moldings are also relatively long.
Diaminodiphenyl methane symmetrically substituted in the 3- and 3'-positions are also known as chain-extenders from U.S. Pat. Nos. 3,036,996 and 3,194,793. In addition to the already mentioned disadvantage of the high melting points of diamines such as these, the simultaneous use of other reaction components, i.e. chlorine-substituted 1,4-bis-(.beta.-hydroxyethyl-mercapto)-benzene or aromatic secondary diamines, is specified as essential in the above-mentioned patents. Combinations such as these, however, lead to products of reduced elasticity which, in addition, are characterized by a marked dependence on the temperature of the shear modulus (oscillating twisting test).
According to German Auslegeschrift No. 2,146,476, the high-melting MOCA is dissolved in a polycyclic hydrocarbon in order to avoid the high-melting temperature problems. This type of procedure, however, results in the undesirable dilution of the elastomer with relatively large quantities of a non-chemically incorporated foreign product.
The object of the present invention is to provide chain-extending agents which, in addition to high reactivity to isocyanates (short in-mold times), have a low melting point. An additional object is to produce elastomers which have excellent mechanical properties.
It has now surprisingly been found that these objects can be achieved by using as chain-extending agents mixtures of asymmetrically substituted diaminodiphenyl methanes which are formed during the condensation of alkyl-substituted aniline mixtures with formaldehyde.